Photonics of supramolecular nanostructures

The results of studying optical and photochemical properties of organic supramolecular nanostructures capable of self-organizing due to specific intermolecular interactions are generalized in the review. The linear and nonlnear optical properties of supramolecular nanostructures of the guest—host type based on cyclodextrins, intramolecular and intermolecular complexes of crown-containing styryl dyes with metal cations, and aggregates of carbocyanine dyes are described. Photolysis reactions in supramolecular nanostructures, including photoisomerization, photocycloaddition, and formation of excimeric and charge-transfer complexes are presented. A possibility of controlling photochemical transformations in these systems by the light and cations of metal salts is shown.     

Spectroscopy of surface-enhanced raman scattering of a complex with charge transfer between a bis-crown-containing stilbene and a bis-ammonium-alkyl derivative of dipyridylethylene

The structure of a charge transfer complex (CTC) formed by a bis-crown-containing stilbene (1) and a dipyridylethylene derivative (2) is studied by surface-enhanced Raman scattering spectroscopy. It is found that an excess of 2 leads to the formation of a 1: 1 CTC structure ([1·2]), whereas an excess of 1 leads to the stabilization of a sandwichlike 2: 1 CTC structure ([1·2·1]). It is also revealed that 1 and diperchlorate of 1-ammoniumpropyl-4-methylpyridinium (5) form a 1: 1 CTC structure, which is much less stable. Analysis of the surface-enhanced Raman scattering data suggests that, in complete agreement with the Mulliken theory, the CTCs under study are ordinary molecular complexes in the ground state and the interaction of a molecular complex with a photon excites the former. The excitation is accompanied by a significant transfer of the electron density from the donor 1 to the acceptor 2 (5). The structural fragments of the molecules responsible for the intermolecular interaction and charge transfer are ascertained using model compounds. The charge transfer in donor-acceptor pairs occurs between the electronic systems of trisubstituted benzene and pyridine. A CTC of the [1·2] or [1·2·1] type contains two equivalent donor-acceptor pairs; however, only one of them is involved in the charge transfer.     

Microstructure fibers as frequency-tunable sources of ultrashort chirped pulses for coherent nonlinear spectroscopy

Microstructure fibers are shown to allow the creation of new tunable sources for femtosecond nonlinear spectroscopy. These fibers provide a high efficiency of frequency upconversion of regeneratively amplified femtosecond pulses of a Cr:forsterite laser, permitting the generation of subpicosecond anti-Stokes pulses with a smooth temporal envelope and a linear positive chirp. These pulses from a microstructure fiber were used to measure the spectra of coherent anti-Stokes Raman scattering (CARS) of toluene solution by cross-correlating these pulses with the femtosecond second-harmonic output of the Cr:forsterite laser in boxcars geometry (XFROG CARS). PACS 42.65.Wi; 42.81.Qb     

An Absorption–Fluorescence Method for Estimation of the Efficiency of Nonradiative Relaxation of Cyanine Dyes

Within the framework of stationary optical spectroscopy, a method for estimation of nonradiative relaxation efficiency for the electronically excited state of a fluorophore is suggested using 3,3-diethylthiacarbocyanine iodide solutions in binary mixtures of toluene and dimethyl sulfoxide (DMSO) as an example. In particular, the quantum yield of dye photoisomerization was found to noticeably decrease upon reducing DMSO content in the mixture.     

Cross-phase-modulation-induced instabilities and frequency shifts in a photonic-crystal fiber

Copropagating fundamental-wavelength and second-harmonic femtosecond pulses of Cr: forsterite laser radiation are used to study cross-phase-modulation-induced instabilities and frequency shifts in a photonic-crystal fiber. Parametric instability of the second-harmonic probe pulse induced through cross-phase modulation by the fundamental-wavelength pump pulse gives rise to distinct sidebands in the spectrum of the probe field transmitted through the fiber. The wavelength of these sidebands was tuned in our experiments within approximately 100 nm by varying the peak power and the delay time of the pump pulse, suggesting a convenient way of controlled parametric spectral transformation of ultrashort laser pulses.This revised version was published online in March 2005. In the previous version, the published online date was missing     

Dynamical systems in the theory of solitons in the presence of nonlocal interactions

The behavior of solitons in models which take into account complex dispersion or nonlocal interaction of nonlinear waves is examined. A method is proposed to reduce this problem to one involving special trajectories (homoclinic and heteroclinic) of the dynamic system. This method involves replacing the nonlinear integrodifferential equation with the differential equations which link the original nonlinear field with the auxiliary linear fields. The interaction of fields in such a model is a local interaction. The number of introduced linear fields is determined by the Laplace transform of the integral operator kernel of the basic integrodifferential equation. The problem involving topological solitons for the nonlocal generalization of the Klein-Gordon equation is considered. Nonlocal interactions are found to lead to a number of singularities (unrestricted increase in the slope of the topological soliton front, break in the solutions, and other singularities).     

Formation of coordination polymeric structures on the basis of 4,4"-dipyridylethylene and Ag+ in solutions

The formation of coordination polymeric chain structures in which silver ions alternate with dipyridylethylene (DPyEt) ligands was studied. In a homogeneous ethanol solution, complex formation of DPyEt with silver cations takes place. The outcome of this reaction depends on the ligand/cation molar ratio, the initial ligand concentration, and the counter-ion type. Conditions were identified under which the coordination polymer is formed as a microdispersed solid precipitating from the solution. The precipitates formed in the DPyEt—AgNO₃ and DPyEt—AgClO₄ systems were investigated by various experimental techniques. The counter-ion was found to be incorporated in the polymer and to influence the structure of the precipitate particles.     

Long-lived phosphorescence of arenes in complexes with cyclodextrins 2. Room-temperature phosphorescence of ternary complexes of naphthalene and phenanthrene with β-cyclodextrin and adamantane derivatives in the presence of oxygen

Long-lived room-temperature phosphorescence (RTP) of arene—β-cyclodextrin (β-CD)— cage hydrocarbon complexes in the presence of oxygen was studied. Naphthalene-d₈, phenanthrene, and fluorene were used as arenes and adamantane, 1,3-dimethyladamantane, diamantane, and diadamantyl were used as the cage hydrocarbons (according to PM3 quantum chemical calculations, the use of these compounds might cause the appearance of long-lived RTP). The RTP lifetime of the naphthalene-d8—β-CD—diadamantyl complex is 11.9 s at 20 °C. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2661–2665, December, 2005.     

Computer simulation of the shape of absorption bands in electronic spectra ofJ-aggregates

The shape of absorption bands of aggregates formed by two, four, and nine molecules of a polymethine dye was calculated by the Monte-Carlo method. The energy of interaction of the molecules in the ground state was simulated using atom-atom potentials, and the energies of interaction between dipole moments of electronic transitions of the monomers were estimated by quantum-chemical methods. In the dimer aggregate the dipole moments of the electronic transitions in the monomers interact weakly; therefore, the electron absorption spectrum should be similar to that of the monomer. On going from the dimer to the aggregates consisting of four and nine monomers, the relative positions of monomers change and this, in turn, increases the energy of interaction between the dipole moments of their electronic transitions, resulting in a red shift characteristic ofJ-aggregates and narrowing of the absorption bands. Translated fromIzvestiya Akademii Nauk Seriya Khimicheskaya. No. 1, pp. 67–69, January, 1997.     

Solvatofluorochromic properties of 2,7-dimethyl-9-(ditolylamino)acridine

Electronic absorption and fluorescence spectra of the acridine dye 2,7-dimethyl-9-(ditolylamino)acridine were studied at room temperature in solvents of different polarity (hexane, toluene, chloroform, tetrahydrofuran, acetonitrile, etc.). The obtained data on the shift of the fluorescence band maximum depending on the solvent polarity were used for the estimation of the dipole moment of 2,7-dimethyl-9-ditolylaminoacridine in the ground and the first excited state.